Cyclic voltammetric studies of electroless cobalt in NaOH

The electrochemical behaviour of electroless cobalt in 1N NaOH was studied at 35, 60 and 85°C by cyclic voltammetry. Three anodic peaks corresponding to the formation of Co(OH)₂/CoO, Co₃O₄, Co OOH were observed. The observed cathodic peaks were due to the reduction of the higher cobalt oxides to Co(OH)₂ and also due to the reduction of Co(OH)₂ to cobalt. The variation of peak potential with sweep rate was found to be appreciable only in the case of anodic peak (I). The total charge Q_T, for the passivation to occur was obtained by estimating the area under the first anodic peak at each sweep rate. It was found that the Q_T value decreases with increase of sweep rate. The increase of peak current with increase of sweep rate has been explained as due to the insufficient time available for the film growth at the reversible potential, and that the dissolution of the metal continues until a potential at which the rate of film growth exceeds that of active dissolution is reached. It has been suggested that the passivating film is CoO while the prepassive film is Co(OH)₂. The shift of the anodic peak (I) potentials to more anodic values compared to that for pure cobalt is probably due to the presence of phosphorus in the cobalt deposit.